1. Field of the Invention
This invention relates to the manufacture of edible food casings derived from animal hide collagen and more particularly to an improved method of tanning the casings in a bath containing a mixture of aluminum ammonium sulfate and monobasic aluminum sulfate.
2. The Prior Art
Collagen casings have been widely accepted as edible food casings for pork sausages.
In the preparation of edible collagen casings, hide collagen derived from animal hides is converted into a finely divided fibrillar form and extruded in the form of a dilute collagen slurry. Usually, the extruded collagen is passed into a sodium sulfate or ammonium sulfate coagulating bath which dehydrates the collagen slurry and forms a coherent collagen film. At this stage in the processing, the salt coagulated collagen film can be handled. However, removal of the ammonium sulfate or other coagulating salt from the film by washing with subsequent wash waters will cause the collagen film to revert to a paste or slurry.
It is therefore necessary to harden or tan the extruded collagen film to permit further processing of the film through the steps of washing, drying, shirring and stuffing.
One of the most widely used methods of tanning collagen casings is described in U.S. Pat. No. 3,123,481 which utilizes a tanning bath containing 3 to 18% by weight of a citrato complex of aluminum ammonium sulfate (alum). One drawback to this process is that alum tanned casings are somewhat stiff and difficult to link after stuffing and have a tendency to split during stuffing. The citric acid chelating or complexing agent present in the bath eventually finds its way into the process effluent and must be removed therefrom as its presence evokes a pollution problem, citric acid being one of the major sources of carbon for bacterial growth in process tanks.